The present invention, in some embodiments thereof, relates to methods of diagnosing and treating cytomegalovirus diseases and, more particularly, but not exclusively, to antibodies capable of same.
Of all the human herpesviruses described to date, infection with cytomegalovirus (CMV) is considered to be the main cause of morbidity and mortality. Approximately 70% of the world population are carriers of the virus. Primary infection with the virus results in a life long persistence in a latent form and is therefore generally asymptomatic in healthy adults. However, some individuals, such as immuno-compromised organ transplant recipients, or individuals infected with human immunodeficiency virus (HIV), are at high risk of developing life threatening CMV disease due to CMV reactivation. In addition, CMV has emerged in recent years as the most important cause of congenital infection in the developed world, commonly leading to mental retardation and developmental disability.
Immunity to CMV is complex and involves humoral and cell-mediated responses. Studies showed that both natural killer (NK) cells and cytotoxic T-lymphocytes (CTLs) are of primary importance in prevention of recurrence. Many gene products participate in generating the CTL response to CMV infection, however, the high level expression frequencies of the viral protein pp65 (e.g., Genbank Accession No. M15120; SEQ ID NO:48) suggests pp65 as the main target of the CTL-mediated immune response. Among all pp65 peptides, CMV specific—CTL activity in HLA-A2 positive individuals was found to be mainly directed to the peptide pp65495-503 (NLVPMVATV; SEQ ID NO:3) (Chee M S et al., 1990).
Cytosolic proteins, usually synthesized in the cells, such as CMV viral proteins, enter the class I MHC pathway of antigen presentation. In the first step, ubiquitinated cytoplasmic proteins are degraded by the proteasome, a cytoplasmic multiprotein complex which generates a large portion of peptides destined for display by class I MHC molecules. Peptides are then delivered from the cytoplasm to the endoplasmic reticulum (ER) by the transporter associated with antigen presentation (TAP) molecules. Newly formed class I MHC dimers in the ER associate with and bind peptides delivered by the TAP. Peptide binding stabilizes class I MHC molecules and permits their movement out of the ER, through the Golgi apparatus, to the cell surface. This pathway ensures that any cell synthesizing viral proteins can be marked for recognition and killing by CD8+ CTL.
Characterization of class I MHC-peptide presentation is essential for understanding the acquired arm of the immune response. The conventional strategy for detecting and studying rare populations of antigen (Ag)-specific CD8+ T cells is the application of tetrameric arrays of class I peptide-MHC complexes (Altman J D., et al., 1996; Lee P P et al., 1999).
The diagnosis of diseases associated with CMV infection such as retinitis, pneumonia, gastrointestinal disorders, and encephalitis is based on clinical, histological, virological and DNA tests.
Current methods of treating CMV in immuno-compromised (e.g., immuno-suppressed) subjects (e.g., HIV patients, bone marrow transplanted subjects), especially CMV retinitis, include anti viral drugs such as Foscarnet (FOSCAVIR®), Cidofovir (VISTIDE®) Valganciclovir (VALCYTE®) Ganciclovir implants (VITRASERT®) Fomivirsen (VITRAVENE®). However, the use of these drugs may be associated with serious side effects such as kidney damage, neutropenia and hypocalcemia. One strategy of directly targeting CMV associated pathologies includes the use of HLA-A2-restricted CD8(+) CTLs directed against pp65. However, attempts to use CMV-specific CD8+ T cell clones for killing CMV-infected retinal pigment epithelial cells have failed (Allart S, et al., 2003; Invest Ophthalmol Vis Sci. 44: 665-71).
Additional background art includes U.S. patent application Ser. Nos. 11/203,137; 11/074,803; 10/510,229; and 11/582,416 to Reiter Y, et al.